Joon-Seol Lee

Exogenous sucrose utilization and starch biosynthesis among sweetpotato cultivars

Three sweetpotato cultivars were investigated for their starch content and amylose/amylopectin ratio. Ym starch contains 87.2% amylopectin and 12.8% amylose, when total starch was calculated as 100%. The Zm cultivar contains 33.6% amylopectin and 18.2% amylose, and its total starch was calculated as 51.8% of that of Ym. The Hm cultivar contains 39.1% amylopectin and 30.5% amylose, and its total starch was 69.6%. We analyzed the expression levels of starch and sucrose biosynthesis-related genes including AGPases a, b, and c; sucrose synthases I and II; starch synthase I; GBSS I; and SBEs I and II. All genes tested in this experiment were detected only in Ym, while several genes showed very faint or no expression in Zm and Hm. We also measured tissue-specific expression of these genes in whole plants of Ym. Most of the genes are expressed in the stem and roots of the plants. Expression profiles of starch synthesis-related genes of the sweetpotato leaves were investigated after supplementing the different concentrations of sucrose solution. All genes in Ym were clearly induced by sucrose, but the expression levels of some of these genes did not change in Zm and Hm. The total starch content of Ym, Zm, and Hm gradually increased over time on addition of 3%, 6%, and 9% sucrose concentrations. The greatest accumulation was observed in Ym at 48h, and it was almost 2.24 times higher than that of the (0%) control, while Zm and Hm showed 1.76 and 1.91 times higher levels of starch, respectively. These results indicate that cooperative expression of all related genes is essential for starch biosynthesis from sucrose. This is the first report on different sucrose contents and the efficiency with which exogenous sucrose switches on gene expression of starch biosynthesis-related genes among cultivars.

Plant Regeneration of Major Cultivars of Sweetpotato (Ipomoea batatas) in Korea via Somatic Embryogenesis

An efficient plant regeneration system of major cultivars of sweetpotato (Ipomoea batatas (L.) Lam.) in Korea via somatic embryogenesis was established. Embryogenic calli were formed from shoot apical meristems of sweetpotato cultivars when cultured on LS medium supplemented with 1 mg/L auxin (2,4-D, picloram, dicamba). Among three kinds of auxin, 1 mg/L 2,4-D showed the highest embryogenic calli induction rate. After 4 weeks of cultures on LS medium supplemented with 1 mg/L 2,4-D, embryogenic calli induction rates of Sinhwangmi, Zami, Yulmi, and White Star were 86%, 78%, 76%, and 80%, respectively. Upon transfer onto LS basal medium, most of somatic embryos developed into plantlets. Regenerated plantlets were transplanted to potting soil and grown to mature plants in a greenhouse.

Contents of low molecular weight antioxidants in the leaves of different sweetpotato cultivars at harvest

Abstract Sweetpotato [ Ipomoea batatas (L.) Lam] leaves are excellent source of low molecular weight antioxidants such as polyphenols, anthocyanins and carotenoids compared to other leafy vegetables. Endogenous antioxidants in sweet-potato help our bodies to prevent ageing, heart diseases and cancer. In this study, to develop the proper cultivars for the functional feed materials, we investigated the contents of anthocyanin, β-carotene, and polyphenols as well as DPPH radical scavenging activity in leaves of 14 different cultivars at the time of the harvest. They showed a diverse antioxidation activity. In DPPH radical scavenging activity, cultivars of Nanjing 9, Yulmi and Shinzami showed higher activity, whereas cv. Huiza 6 showed the lowest. Cultivars of Shinzami and Shinhwangmi had the highest anthocyanin (3.5 mg/g fr wt) and polyphenol (15.8 mg/g fr wt) content, respectively. Interestingly, there was a high correlation between cultivars with colorful pigments in storage roots and antioxidants activity in leaves. These results suggest that sweetpotato leaves with high antioxidant activity at harvest would be suitable for functional feed materials.